net: enetc: set up XDP program under enetc_reconfigure()

Offloading a BPF program to the RX path of the driver suffers from the
same problems as the PTP reconfiguration - improper error checking can
leave the driver in an invalid state, and the link on the PHY is lost.

Reuse the enetc_reconfigure() procedure, but here, we need to run some
code in the middle of the ring reconfiguration procedure - while the
interface is still down. Introduce a callback which makes that possible.

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>